The present invention relates to lithium fluoroalkyl-phosphates, a process for preparing them and their use as electrolyte salts in batteries, capacitors, supercapacitors and electrolytic cells.
The spread of portable electronic appliances such as laptop and palmtop computers, mobile telephones and video cameras, and thus also the need for light and powerful batteries has increased dramatically world-wide in recent years.
In view of this jump in the demand for batteries and the associated ecological problems, the development of rechargeable batteries having a long life is steadily increasing in importance.
Since the early 1990s, rechargeable lithium ion batteries have been commercially available. Most of these lithium ion batteries employ lithium hexafluorophosphate as electrolyte salt. However, this lithium salt is an extremely hydrolysis-sensitive compound having a low thermal stability, so that the corresponding lithium batteries can, owing to this property of the salt, only be produced by very complicated and thus also very costly methods.
The sensitivity of this lithium salt also reduces the life and the performance of these lithium batteries and also impairs their use under extreme conditions, e.g. at high temperatures.
There has therefore been no lack of attempts to provide lithium salts having improved properties. Thus, U.S. Pat. Nos. 4,505,997 and 9,202,966 describe the use of lithium bis(trifluoromethylsulfonyl)imide and lithium tris(trifluoromethylsulfonyl)methanide salts as electrolyte salts in batteries. Both salts display high anodic stability and form solutions having a high conductivity with organic carbonates. However, lithium bis(tri-fluoromethylsulfonyl)imide has the disadvantage that it does not sufficiently passivate the aluminium metal which functions as cathodic terminal lead in lithium batteries.
Lithium tris(trifluoromethylsulfonyl)methanide, on the other hand, is very expensive to produce and purify, so that the use of this salt as electrolyte salt in batteries greatly increases the production costs for such lithium batteries.
DE 196 411 38 teaches the use of lithium fluorophosphates preferably having perfluorinated or partially fluorinated ethyl and isopropyl groups as ligands. Although the thermal stability and the hydrolysis resistance of these lithium salts are significantly higher than those of lithium hexafluorophosphate, they hydrolyse within days in the presence of small traces of water, so that when using these electrolyte salts, too, the performance and life of the batteries based on these salts are reduced.
It is therefore an object of the invention to provide electrolyte salts which display no or only very slight signs of hydrolysis over a long period of time. A further object of the invention is to extend or improve the life and the performance of batteries, capacitors, supercapacitors and electrolytic cells.
This object is surprisingly achieved by the provision of lithium fluoroalkylphosphates of the general formula (I),
Li+[PFx(CyF2y+lxe2x88x92zHz)6xe2x88x92x]xe2x88x92xe2x80x83xe2x80x83(I)
where
1xe2x89xa6xxe2x89xa65
3xe2x89xa6yxe2x89xa68 and
0xe2x89xa6zxe2x89xa62y+1
and the ligands (CyF2y+lxe2x88x92zHz) can be identical or different, with the exception of compounds of the general formula (Ixe2x80x2)
Li+[PFa(CHbFc(CF3)d)e]xe2x88x92xe2x80x83xe2x80x83(Ixe2x80x2)
in which a is an integer from 2 to 5, b=0 or 1, c=0 or 1, d=2 and e is an integer from 1 to 4, with the provisos that b and c are not simultaneously 0 and the sum of a+e is 6 and the ligands (CHbFc(CF3)d) can be identical or different.
Preference is given to lithium fluoroalkylphosphates of the general formula (I) in which 1xe2x89xa6xxe2x89xa65, 3xe2x89xa6yxe2x89xa68 and z=0.
Particular preference is given to the following lithium fluoroalkylphosphates of the general formulae (I):
Li+[F6xe2x88x92xP(CF2xe2x80x94CF2xe2x80x94CF3)x]xe2x88x92
and
Li+[F6xe2x88x92xP(CF2xe2x80x94CF2xe2x80x94CF2xe2x80x94CF3)x]xe2x88x92
in which 1 xe2x89xa6xxe2x89xa63 in each case.
The lithium fluoroalkylphosphates of the general formula (I) can be used, either in pure form or in the form of their mixtures, as electrolyte salts in primary and secondary batteries, capacitors, supercapacitors and electrolytic cells. It is also possible to use the lithium fluoroalkylphosphates of the invention together with further lithium salts known to those skilled in the art as electrolyte salt. The lithium fluoroalkylphosphates of the invention are preferably used in pure form as electrolyte salt, since particularly good reproducibility of the electrochemical properties can be achieved in this way.
The invention likewise provides a process for preparing the novel lithium fluoroalkylphosphates of the general formula (I), which is characterised in that at least one compound of the general formula
HmP(CnH2n+1)3xe2x88x92mxe2x80x83xe2x80x83(III),
OP(CnH2n+1)3xe2x80x83xe2x80x83(IV),
ClmP(CnH2n+1)3xe2x88x92mxe2x80x83xe2x80x83(V),
FmP(CnH2n+1)3xe2x88x92mxe2x80x83xe2x80x83(VI),
xe2x80x83CloP(CnH2n+1)5xe2x88x92oxe2x80x83xe2x80x83(VII)
or
FoP(CnH2n+1)5xe2x88x92oxe2x80x83xe2x80x83(VIII),
where in each case
0xe2x89xa6mxe2x89xa62
3xe2x89xa6nxe2x89xa68 and
0xe2x89xa6oxe2x89xa64,
is fluorinated by electrolysis in hydrogen fluoride, the resulting mixture of fluorination products is fractionated by extraction, phase separation and/or distillation, preferably by fractional distillation, and the resulting fluorinated alkylphosphorane is reacted with lithium fluoride in an aprotic solvent or solvent mixture in the absence of moisture, and the resulting novel lithium fluoroalkylphosphate of the general formula (I) is purified and isolated by customary methods.
The electrolysis is preferably carried out at a temperature of from xe2x88x9220 to +40xc2x0 C., particularly preferably from xe2x88x9210 to +10xc2x0 C. and very particularly preferably at from xe2x88x925 to +5xc2x0 C.; the pressure is preferably from 0.5 to 3 bar, particularly preferably from 0.5 to 1.5 bar and very particularly preferably atmospheric pressure.
The applied voltage during the electrolysis is preferably from 4 to 6 V, particularly preferably from 4.5 to 5.5 V, and the current density is preferably from 0.2 to 5 A/dm2, particularly preferably from 0.2 to 2 A/dm2 and very particularly preferably from 0.5 to 1.5 A/dm2.
The compounds of the general formulae (V) and (VII) can also be reacted with inorganic fluorinating agents, preferably with SbF3, SbF5, MoF5, VF5 or mixtures thereof so as to replace the chlorine atoms by fluorine atoms prior to the electrolysis in hydrogen fluoride. The reaction conditions under which these fluorinations are carried out are known to those skilled in the art.
The reaction of the fluorinated alkylphosphorane with lithium fluoride is preferably carried out at a temperature of from xe2x88x9235 to 60xc2x0 C., particularly preferably from xe2x88x9220 to +50xc2x0 C. and very particularly preferably from xe2x88x9210 to 25xc2x0 C.
Solvents used for the reaction of the fluorinated alkylphosphoranes with lithium fluoride are preferably carbonates, nitrites, ethers, esters, amides, sulfones or mixtures thereof.
Particular preference is given to using solvents or solvent mixtures which are suitable for direct use in a primary or secondary battery, a capacitor, a supercapacitor or an electrolytic cell, for example dimethyl carbonate, diethyl carbonate, propylene carbonate, ethylene carbonate, ethyl methyl carbonate, methyl propyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, methyl acetate, y-butyrolactone, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, ethyl butyrate, dimethylsulfoxide, dioxolane, sulfolane, acetonitrile, acrylonitrile, tetrahydrofuran, 2-methyltetrahydrofuran or mixtures thereof. The electrolytes obtained in this way are suitable for use in primary batteries, secondary batteries, capacitors, supercapacitors and electrolytic cells and are likewise provided by the present invention.
The concentration of the lithium fluoroalkylphosphate(s) of the invention in these electrolytes is preferably from 0.01 to 3 mol/l, particularly preferably from 0.01 to 2 mol/l and very particularly preferably from 0.1 to 1.5 mol/l.
The invention also provides primary batteries, secondary batteries, capacitors, supercapacitors and electrolytic cells containing at least one novel lithium fluoroalkylphosphate of the general formula (I) and, if desired, further lithium salts and/or additives. These further lithium salts and additives are known to those skilled in the art, for example from Doron Aurbach, Nonaqueous Electrochemistry, Marc Dekker Inc., New York 1999; D. Linden, Handbook of Batteries, Second Edition, McGraw-Hill Inc., New York 1995 and G. Mamantov and A. I. Popov, Chemistry of Nonaqueous Solutions, Current Progress, VCH Verlagsgemeinschaft, Weinheim 1994. They are hereby incorporated by reference into the present disclosure. The lithium fluoroalkylphosphates of the invention can be used with customary electrolytes. Examples of suitable electrolytes are those comprising electrolyte salts selected from the group consisting of LiPF6, LiBF4, LiClO4, LiAsF6, LiCF3SO3, LiN(CF3SO2)2 or LiC(CFSO2)3 mixtures thereof. The electrolytes may further comprise organic isocyanates (DE 199 44 603) to reduce the water content. Likewise, the electrolytes may further comprise organic alkali metal salts (DE 199 10 968) as additives. Suitable alkali metal salts are alkali metal borates of the general formula
Li+Bxe2x88x92(OR1)m(OR2)p
where
m and p are 0, 1, 2, 3 or 4 with m+p 4 and
R1 and R2 are identical or different,
if desired are joined directly to one another by a single or double bond,
and are, in each case individually or together, an aromatic or aliphatic carboxylic, dicarboxylic or sulfonic acid group, or
are, in each case individually or together, an aromatic ring selected from the group consisting of phenyl, naphthyl, anthracenyl and phenanthrenyl, which may be unsubstituted or monosubstituted to tetrasubstituted by A or Hal, or
are, in each case individually or together, a heterocyclic aromatic ring selected from the group consisting of pyridyl, pyrazyl and bipyridyl, which may be unsubstituted or monosubstituted to trisubstituted by A or Hal, or
are, in each case individually or together, an aromatic hydroxy acid selected from the group consisting of aromatic hydroxycarboxylic acids and aromatic hydroxysulfonic acids, which may be unsubstituted or monosubstituted to tetrasubstituted by A or Hal, and
Hal is F, Cl or Br and
A is alkyl having from 1 to 6 carbon atoms, which may be monohalogenated to trihalogenated.
Likewise suitable are alkali metal alkoxides of the general formula
Li+ORxe2x88x92
where
R is an aromatic or aliphatic carboxylic, dicarboxylic or sulfonic acid group, or
is an aromatic ring selected from the group consisting of phenyl, naphthyl, anthracenyl and phenanthrenyl, which may be unsubstituted or monosubstituted to tetrasubstituted by A or Hal, or
is a heterocyclic aromatic ring selected from the group consisting of pyridyl, pyrazyl and bipyridyl, which may be unsubstituted or monosubstituted to trisubstituted by A or Hal, or
is an aromatic hydroxy acid selected from the group consisting of aromatic hydroxycarboxylic acids and aromatic hydroxysulfonic acids, which may be unsubstituted or monosubstituted to tetrasubstituted by A or Hal, and
Hal is F, Cl or Br, and
A is alkyl having from 1 to 6 carbon atoms, which may be monohalogenated to trihalogenated.
Lithium complex salts of the formula 
where
R1 and R2 are identical or different, if desired are joined directly to one another by a single or double bond, and are, in each case individually or together, an aromatic ring selected from the group consisting of phenyl, naphthyl, anthracenyl and phenanthrenyl, which may be unsubstituted or monosubstituted to hexasubstituted by alkyl (C1 to C6), alkoxy groups (C1 to C6), or halogen (F, Cl, Br),
or are, in each case individually or together, an aromatic heterocyclic ring selected from the group consisting of pyridyl, pyrazyl and pyrimidyl, which may be unsubstituted or monosubstituted to tetrasubstituted by alkyl (C1 to C6), alkoxy groups (C1 to C6) or halogen (F, Cl, Br), or are, in each case individually or together, an aromatic ring selected from the group consisting of hydroxybenzenecarboxyl, hydroxynaphthalenecarboxyl, hydroxybenzenesulfonyl and hydroxynaphthalenesulfonyl, which may be unsubstituted or monosubstituted to tetrasubstituted by alkyl (C1 to C6), alkoxy groups (C1 to C6) or halogen (F, Cl, Br), R3-R6 can, in each case individually or pairwise, if desired joined to one another directly by a single or double bond, have the following meanings:
1. Alkyl (C1 to C6), alkyloxy (C1 to C6) or halogen (F, Cl, Br)
2. an aromatic ring selected from the groups phenyl, naphthyl, anthracenyl and phenanthrenyl, which may be unsubstituted or monosubstituted to hexasubstituted by alkyl (C1 to C6), alkoxy groups (C1 to C6) or halogen (F, Cl, Br), pyridyl, pyrazyl and pyrimidyl, which may be unsubstituted or monosubstituted to tetrasubstituted by alkyl ((C1 to C6), alkoxy groups (C1 to C6) or halogen (F, Cl, Br), which are prepared by the following method (DE 199 32 317)
a) 3-, 4-, 5-, 6-substituted phenol is admixed in a suitable solvent with chlorosulfonic acid, b) the intermediate from a) is reacted with chlorotrimethylsilane, filtered and fractionally distilled,
c) the intermediate from b) is reacted with lithium tetramethoxyborate(1-) in a suitable solvent and the end product is isolated therefrom, may also be present in the electrolyte.
Likewise, the electrolytes may comprise compounds of the following formula (DE 199 41 566)
[([R1(CR2R3)k]lAx)yKt]+ xe2x88x92N(CF3)2
where
Kt=N, P, As, Sb, S, Se
A=N, P, P(O), 0, S, S(O), SO2, As, As(O) Sb, Sb(O)
R1, R2 and R3 may be identical or different and are each H, halogen, substituted and/or unsubstituted alkyl CnH2n+1, substituted and/or unsubstituted alkenyl having 1-18 carbon atoms and one or more double bonds, substituted and/or unsubstituted alkynyl having 1-18 carbon atoms and one or more triple bonds, substituted and/or unsubstituted cycloalkyl CmH2mxe2x88x921, monosubstituted or polysubstituted and/or unsubstituted phenyl, substituted and/or unsubstituted heteroaryl,
where A may be included in various positions in R1, R2 and/or R3,
Kt may be included in a carbocyclic or heterocyclic ring,
the groups bound to Kt may be identical or different, and where
n=1-18
m=3-7
k=0, 1-6
l=1 or 2 in the case of x=1 and 1 in the case of x=0
x=0, 1
y=1-4.
The process for preparing these compounds is characterized in that an alkali metal salt of the general formula
D+xe2x88x92N(CF3)2xe2x80x83xe2x80x83(II)
where D+ is selected from the group consisting of the alkali metals, is reacted in a polar organic solvent with a salt of the general formula
[([R1(CR2R3)k]lAx)yKt]+xe2x88x92Exe2x80x83xe2x80x83(III)
where
Kt, A, R1, R2, R3, k, l, x and y are as defined above and
xe2x88x92E is Fxe2x88x92, Clxe2x88x92, Brxe2x88x92, Ixe2x88x92, BF4xe2x88x92, ClO4xe2x88x92, AsF6xe2x88x92, SbF6xe2x88x92 or PF6xe2x88x92.
It is also possible to use electrolytes comprising compounds of the general formula (DE 199 53 638)
Xxe2x80x94(CYZ)mxe2x80x94SO2N(CR1R2R3)2
where
X is H, F, Cl, CnF2n+1, CnF2nxe2x88x921, (SO)2)kN(CR1R2R3)2 
Y is H, F, Cl
Z is H, F, Cl
R1,R2,R3 is H and/or alkyl, fluoroalkyl, cycloalkyl
m is 0-9 and, if X=H, mxe2x89xa00
n is 1-9
k is 0 if m=0, and k=1 if m=1-9,
prepared by reacting partially fluorinated or perfluorinated alkylsulfonylfluorides with dimethylamine in organic solvents, and also complex salts of the general formula (DE 199 51 804)
Mx+[EZ]yxe2x88x92x/y
where:
x, y are 1, 2, 3, 4, 5, 6
Mx+ is a metal ion
E is a Lewis acid selected from the group consisting of
BR1R2R3, AlR1R2R3, PR1R2R3R4R5, AsR1R2R3R4R5, VR1R2R3R4R5,
R1 to R5 are identical or different, if desired are joined directly to one another by a single or double bond, and may be, in each case individually or together, a halogen (F, Cl, Br),
an alkyl or alkoxy radical (C1 to C8) which may be partially or fully substituted by F, Cl, Br, an aromatic ring, if desired bound via oxygen, selected from the group consisting of phenyl, naphthyl, anthracenyl and phenanthrenyl, which may be unsubstituted or monosubstituted to hexasubstituted by alkyl (C1 to C8) or F, Cl, Br, an aromatic heterocyclic ring, if desired bound via oxygen, selected from the group consisting of pyridyl, pyrazyl and pyrimidyl, which may be unsubstituted or monosubstituted to tetrasubstituted by alkyl ((C1 to C8) or F, Cl, Br, and Z is OR6, NR6R7, CR6R7R8, OSO2R6, N(SO2R6)(SO2R7), C(SO2R6)(SO2R7)(SO2R8), OCOR6, where
R6 to R8 are identical or different, if desired are joined directly to one anther by a single or double bond, and are, in each case individually or together,
a hydrogen or as defined for R1 to R5, prepared by reacting a corresponding boron or phosphorus Lewis acid-solvent adduct with a lithium or tetraalkylammonium imide, methanide or triflate.
Borate salts (DE 199 59 722) of the general formula 
where
M is a metal ion or tetraalkylammonium ion
x, y are 1, 2, 3, 4, 5 or 6
R1 to R4 are identical or different alkoxy or carboxyl groups (C1 to C8) which may be joined directly to one another by a single or double bond may also be present. These borate salts are prepared by reacting lithium tetraalkoxyborate or a 1:1 mixture of lithium alkoxide and a boric ester in an aprotic solvent with a suitable hydroxyl or carboxyl compound in the ratio 2:1 or 4:1.
These electrolytes can be used in electrochemical cells having cathodes comprising customary lithium intercalation and insertion compounds or else cathode materials consisting of lithium mixed oxide particles and coated with one or more metal oxides (DE 199 22 522) by suspending the particles in an organic solvent, admixing the suspension with a solution of a hydrolysable metal compound and a hydrolysis solution and then filtering off, drying and, if desired, calcining the coated particles. They can also consist of lithium mixed oxide particles which are coated with one or more polymers (DE 199 46 066) and obtained by a process in which the particles are suspended in a solvent and the coated particles are subsequently filtered off, dried and, if desired, calcined.
The lithium fluoroalkylphosphates of the invention have the advantage that they display no or virtually no signs of hydrolytic decomposition over a very long period of time in the presence of water. Furthermore, they have a high thermal stability. These properties make it possible to use batteries, capacitors, supercapacitors and electrolytic cells which contain these electrolyte salts under extreme conditions, e.g. at high temperatures, without their life and performance being impaired by these conditions. Furthermore, the corresponding batteries, capacitors, supercapacitors and electrolytic cells display very good voltage constancy and unimpaired function over many charge-discharge cycles and also have low production costs.
The use of the lithium fluoroalkylphosphates of the invention in large lithium ion batteries as are used, for example, in electric road vehicles or hybrid road vehicles is likewise very advantageous, since damage to the batteries, for example in the case of an accident, even if contact with water occurs, for example due to atmospheric moisture or water used in fire fighting, results in no formation of toxic and highly corrosive hydrogen fluoride.
Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The following preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever.
In the foregoing and in the following examples, all temperatures are set forth uncorrected in degrees Celsius; and, unless otherwise indicated, all parts and percentages are by weight.
The entire disclosures of all applications, patents and publications, cited above, and of corresponding German Application No. 10 008 955.0, filed Feb. 25, 2000, are hereby incorporated by reference.